This application is based upon and claims the benefit of Japanese Patent Applications No. 11-307656 filed on Oct. 28, 1999, and No. 2000-268960 filed on Sep. 5, 2000, the contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to a substrate processing technique for formation of a semiconductor element.
2. Description of the Related Art
As shown in FIG. 18, to form a doping layer 101 uniform in a depth direction at a desired position in a silicon substrate 100 not only attracts attention as a substrate structure effective in lowering an on resistance of a high withstand voltage MOS device disclosed in U.S. Pat. No. 5,438,215, but also is effective to enable high integration in the depth direction by effectively using the depth direction of the substrate.
As a method of forming the doping layer 101, it is conceivable to use dopant diffusion from the surface, or a method of dopant ion implantation and heat treatment, which is conventionally generally used in a silicon semiconductor process. However, the depth B of the doping layer 101 is controlled by the diffusion rate of the dopant impurity. Thus, in a generally used heat treatment time, it is possible to merely form the doping layer 101 of a depth of several xcexcm from the surface. Besides, since the diffusion of the dopant advances isotropically, the diffusion advances not only in the depth direction but also in the lateral direction, and the doping layer 101 having a lateral extension A comparable to the depth is eventually obtained. Thus, in the doping layer formation by the conventional heat diffusion, an aspect ratio (=B/A) does not exceed xe2x80x9c1xe2x80x9d in principle, and the structure in formation of a device is restricted.
On the other hand, xe2x80x9cA new generation of high power MOSFETs breaks the limit line of siliconxe2x80x9d IEDM98 Proc. (1998) by G. Deboy et al., proposes the following method. That is, first, as shown in FIGS. 19A and 19B, an epitaxial film 111a is formed on a substrate 110 by epitaxial growth, and as shown in FIG. 19C, a doping layer 112a is formed by partial dopant ion implantation with photolithography and heat diffusion treatment. Next, as shown in FIGS. 20A and 20B, the epitaxial growth, partial ion implantation, and heat diffusion treatment are repeated. As a result, as shown in FIG. 20C, a doping layer 112 extending in the depth direction is formed. According to this method, since the depth of the formed doping layer (doping layer extending in the depth direction) 112 is determined by epitaxial growth thickness, it is not controlled by the diffusion length of the dopant.
However, since the extension in the lateral direction is controlled through the diffusion length of one diffusion treatment, the lateral extension equivalent to the film thickness of one epitaxial growth becomes a processing limit. Thus, in the case where a deeper profile is desired to be formed, it is sufficient if the epitaxial film thickness is increased. However, in order to suppress the extension in the lateral direction, it is necessary to thin the thickness of one epitaxial growth. As a result, the number of times of the epitaxial growth and diffusion treatment of the dopant is increased, and the manufacturing cost of a substrate is increased.
Besides, a processing method proposed in EP-A-53854 is shown in FIGS. 21A-21C. First, as shown in FIGS. 21A and 21B, trenches 121 are formed in a substrate 120, and as shown in FIG. 21C, an epitaxial layer 122 of a desired dopant concentration is filled in the inside of each of the trenches 121. Accordingly, a profile in the depth direction is formed. In this processing method, substrate formation can be made by a trench forming step and an epitaxial growth step, and the number of steps is small and it is expected that throughput is improved. Further, since the shape of the doping layer is almost coincident with a trench shape, it is conceivable that an arbitrary shape with high aspect ratio can be formed as compared with the foregoing method of repeating the epitaxial growth and the dopant diffusion plural times.
However, as expected important problems in the case of trench filling epitaxial growth, void-less trench filling, defect-less epitaxial growth, and high controllability of doping concentration can be pointed out. On the other hand, in the present circumstances, a study of the trench filling epitaxial growth has not been sufficiently carried out, and proper measures against the problems and a manufacturing method are not clear.
Besides, there is a selective epitaxial method as an epitaxial growth technique similar to the trench filling epitaxial growth. The selective epitaxial method is a method in which as shown in FIGS. 22A and 22B, an oxide film 131 having opening portions 132 is disposed on a substrate 130, and as shown in FIG. 22C, epitaxial films 133 are grown only on portions where the surface of the silicon substrate 130 is exposed.
Thus, the structure in which the epitaxial films 133 are filled in the oxide film opening portions 132 is eventually obtained. The selective epitaxial technique has an object to form such a structure that the epitaxial films 133 are made device formation regions of CMOS and the oxide film 131 which is a mask is made element separation regions. Also in the selective epitaxial growth, void-less trench filling and defect-less epitaxial growth have been studied as the main technical problems.
The present invention has been made in view of the above problems. An object of the present invention is to provide a noble structure for a semiconductor substrate that has a semiconductor layer extending in a depth direction of the semiconductor substrate with a uniform concentration profile, and a method for manufacturing the same.
According to a first aspect of the present invention, a semiconductor substrate has a trench having a first width at a bottom thereof and a second width at an opening portion thereof larger than the first width. The trench is filled with a semiconductor layer having a dimension in a normal line direction with respect to a surface of the semiconductor substrate larger than a lateral dimension thereof that is a dimension in a lateral direction on an arbitrary plane parallel to the surface of the semiconductor substrate intersecting the trench.
According to a second aspect of the present invention, a semiconductor substrate has a semiconductor layer filled in a trench and having a dimension in a normal line direction with respect to a surface of the semiconductor substrate larger than a lateral dimension thereof that is a dimension in a lateral direction on an arbitrary plane parallel to the surface of the semiconductor substrate intersecting the trench. Further a conductive material is filled in the semiconductor layer in the trench for taking a potential of the semiconductor layer.
According to a third aspect of the present invention, a semiconductor substrate is manufactured by forming a trench in a semiconductor substrate; forming a first epitaxial layer on a surface of the semiconductor substrate and in the trench; etching a part of the first epitaxial film; and forming a second epitaxial film in the trench so that the trench is filled with the first and second epitaxial films.
According to a forth aspect of the present invention, a semiconductor substrate is manufactured by forming a trench; filling an amorphous semiconductor film in the trench; single-crystallizing the amorphous semiconductor film through a solid phase reaction; and flattening the surface of the semiconductor substrate.
According to a fifth aspect of the present invention, a semiconductor substrate is manufactured by forming a trench; forming an epitaxial film on a surface of the semiconductor substrate and in the trench; forming a conductive material film on the epitaxial film so that the conductive material film is filled in the epitaxial film in the trench; and flattening the surface of the semiconductor substrate.
According to a sixth aspect of the present invention, a semiconductor substrate is manufactured by forming a trench having a first depth in a semiconductor substrate; forming an epitaxial film on a surface of the semiconductor substrate and in the trench; and removing the epitaxial film on the surface of the semiconductor substrate, and a surface portion of the semiconductor substrate so that the trench has a second depth smaller than the first depth and is completely filled with the epitaxial film.
According to a seventh aspect of the present invention, when an epitaxial film is formed to fill a trench, a relation of B/xcex1 less than F/2xcex2 is satisfied, in which:
xcex1 is a first growth rate of the epitaxial film on a bottom of the trench;
xcex2 is a second growth rate of the epitaxial film on a side of the trench;
F is a width at an opening portion of the trench; and
B is a depth of the trench.
Thus, the present invention provides various constructions for a semiconductor substrate that has a semiconductor layer extending in an depth direction of the substrate with a uniform concentration profile with a high aspect ratio and a method for manufacturing the semiconductor substrate efficiently without generating any voids, crystal defects and the like.